39 
Lacaze-Duthier’s observations, published more than twenty 
years ago (Ann. d. Sc. Nat. 1854. Organes genitaux des 
Acephales Lamellibranches.; and, Comptes rendus, 1855, x 4, 
415-420. Des organes de la generation de Phuitre), are very 
similar to those of Mobius. He says that at any given time 
each oyster is almost exclusively male or almost exclusively 
female, and he thinks that the young oysters are functionally 
male, and become female as they grow older. 
As I have already stated, I have found oysters only one 
year old which contained ripe eggs, and eggs only, and others 
of the same age which were exclusively male, and I have suc- 
ceeded in fertilizing the eggs of the one with the fluid of the 
other. This observation, which is corroborated by Gerbe’s 
statement (Zool. Record, 1876, xiii., Mol. p. 62), that among 
435 European oysters one year old, he found 35 with young ; 
127 with ripe eggs, and 189 with ripe semen, seems to be 
sufficient to show the incorrectness of Lacaze-Duthier’s con- 
jecture that the functionally male condition precedes the func 
tionally female condition. 
MANNER OF FERTILIZATION. 
Although the American oyster seems well adapted, like the 
European species, and various other marine and fresh- water 
Lamellibranchs, to draw into its mantle-chamber, with the sea- 
water, the spermatozoa discharged from the mantle-chambers 
of neighboring oysters, and thus to bring about the fertiliza- 
tion of the eggs inside the cavity of the shell, this does not 
seem to occur. 
I have carefully searched the gills and mantles of more than 
a thousand oysters at a time when the reproductive organs 
were plainly seen to be discharging their ripe contents, and 
have not found a single fertilized egg or embryo in any part 
of the mantle-chamber, in or on the gills, or anywhere else 
inside the shell. This negative evidence, together with the 
fact that the eggs can be hatched after they have been arti- 
ficially removed from the ovaries seems sufficient to prove, in 
the absence of all evidence to the contrary, that the eggs of 
the American oyster undergo development in the open ocean. 
